Many portable devices such as portable computers use backlight assemblies for illuminating displays such as liquid crystal displays. Backlight assemblies typically include a light pipe that couples light from a light source such as one or more LEDs into the display using a process called total internal reflection (TIR).
When light within a light pipe impinges on a front or rear surface of the light pipe at the proper angle, the light exits the light pipe and passes through one or more layers of additional light diffusing, directing or turning films before entering and illuminating the display.
In order to improve brightness, a number of prior art techniques have been used. For example, since the display to be illuminated is adjacent a front of the light pipe, the back of the light pipe is typically coated with a reflective material. Another technique is to limited egress of light out of the front surface of the light pipe to only that light that is substantially normal to the front surface of the light pipe.
One method to accomplish this objective has been to leave a small air gap between the light pipe and any covering film. The air gap provides a significant change in the index of refraction that causes light at low angles to be reflected back into the light pipe.
While prior art methods have proven to be somewhat effective, significant improvements can still be made. Accordingly, a need exists for better methods of coupling light into back light assemblies.